updated 5/5/2008 1:33:10 PM ET 2008-05-05T17:33:10

A small earthquake shook the St. Louis area Monday, causing some residents to awake to a disconcerting rumbling for the second time in less than a month.

There were no reports of damage or injuries.

The epicenter of the quake at 6:25 a.m. was in southwest St. Louis County — just the sixth documented earthquake over the last two centuries centered in St. Louis or the county. The U.S. Geological Survey estimated its magnitude at 2.7. Seismologists at Saint Louis University believe it was a 2.8 or a 2.9.

Several residents reportedly heard a "boom" as the ground began to shake. The Geological Survey received hundreds of reports from people who felt it, mostly in the St. Louis area but some in Illinois.

On April 18, a magnitude 5.2 earthquake shook much of the Midwest, including parts of St. Louis. Its epicenter was in southern Illinois near the Indiana border, about 140 miles from St. Louis. More than two dozen aftershocks followed.

Until Monday, the most recent earthquake centered near St. Louis was a magnitude 2.4 temblor on Jan. 15, 1998, with an epicenter of Kirkwood.

The most memorable earthquakes felt in St. Louis were not centered here. In 1811 and 1812, quakes along the New Madrid fault line registered at magnitude 8.0 and above, reportedly causing the Mississippi River to flow backward. Those tremors could be felt as far away as New England.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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